This invention is generally directed to toner compositions, and developer compositions and the use of these compositions in electrostatographic imaging systems. More specifically, the present invention is directed to toner compositions, including magnetic toner compositions and colored toner compositions containing a thermally stable tetrafluoroborate charge enhancing additive. Positively charged toner compositions containing these additives are particularly useful in electrostatographic imaging systems having incorporated therein a Viton coated fuser roll, since the tetrafluoroborates involved do not react with the Viton, causing undesirable decomposition thereof, and adversely affecting image quality.
Positively charged toner compositions containing charge enhancing additives are generally known. Thus, for example, there is disclosed in U.S. Pat. No. 3,893,935, the use of certain quaternary ammonium compounds as charge control agents for electrostatic toner compositions. This patent teaches the incorporation of a specific quaternary ammonium compound into toner particles for the purpose of obtaining particles exhibiting relatively high uniform and stable net toner charge when mixed with a suitable carrier vehicle. A similar teaching is disclosed in U.S. Pat. No. 4,079,014 with the exception that a different charge control additive is selected, namely, a diazo type material.
Further there is described in U.S. Pat. No. 4,298,672 developer compositions containing as a charge enhancing additive an alkyl pyridinium compound including, for example, cetyl pyridinium chloride. This patent also discloses that the anion on the alkyl pyridinium material can be selected from halides, sulfates, sulfonates, nitrate, and borate. While these developer compositions are sufficient for their intended purposes it appears that the alkyl pyridinium compounds react with the polymer contained on Viton fuser rolls causing decomposition thereof. Other patents disclosing charge control additives include U.S. Pat. Nos. 3,944,493, 4,007,293, and 4,079,014.
Several prior art charge control agents of the prior art interact with certain fuser rolls, such as for example, the Viton fuser roll, used in electrostatographic systems. This interaction causes the fuser to be adversely affected, resulting in deterioration of the image quality. For example, Viton fuser rolls discolor and turn black, develop multiple surface cracks and harden, when certain charge control additive compounds are contained in the toner mixture.
One Viton fuser roll selected for use in electrostatographic copying machines, is comprised of a soft roll fabricated from lead oxide, and duPont Viton E-430 resin, a vinylidene fluoride hexafluoropropylene copolymer. This roll contains approximately 15 parts of lead oxide, and 100 parts of Viton E-430, which mixture is blended and cured on the roll substrate at elevated temperatures. Apparently the function of the lead oxide is to generate unsaturation by dehydrofluorination for crosslinking, and to provide release mechanisms for the toner composition. Excellent image quality has been obtained with Viton fuser rolls, however, in some instances there results a toner fuser compatibility problem when charge control agents are part of the toner mixture. For example, it appears that certain specific charge control additives, such as quaternary ammonium compounds, and alkyl pyridinium compounds, including cetyl pyridinium chloride, react with the Viton of the Viton fuser roll. For example, cetyl pyridinium chloride when part of the toner mixture appears to be catalytically decomposed by the lead oxide contained in the fuser roll, resulting in a highly unsaturated compound, which polymerizes and condenses with the unsaturated Viton E-430 material. In view of this, the Viton fuser roll turns black, develops multiple surface cracks, and the surface thereof hardens, thereby resulting in image quality deterioration.
The art of xerography continues to advance and recently, there has been disclosed layered photoresistive imaging devices comprised of generating layers and transport layers. These devices usually are charged negatively, rather than positively as is the situation with the selenium photoreceptor, thereby requiring a toner composition that is positively charged in order that the toner particles may be suitable attracted to the electrostatic latent image contained on the photoreceptor surface. In view of this development, extensive efforts have been devoted to obtaining developer compositions containing toner resins which are positively charged. Generally, charge control additives are selected for the purpose of imparting the appropriate positive charge to the toner resins. While many charge control additives are known, there continues to be a need for new charge control additives, particularly those additives which will not interact with Viton type fuser rolls. Additionally, there continues to be a need for charge control additives which are thermally stable at high temperatures. Moreover, there continues to be a need for positively charged toner and developer compositions which are humidity insensitive since it is known that moisture contained in the atmosphere, or moisture from many other sources, can effect adversely the electrical properties of the toner compositions involved.